I was just sent this link this morning: https://finance.yahoo.com/news/amazon-introduces-aws-graph-database-171648039.html.
I personally think Dgraph has an edge due to GraphQL±. From a cursory search, I’m not sure if Neptune has transactions, although https://aws.amazon.com/neptune/ states “With Amazon Neptune, you can use relationships to process financial and purchase transactions…”. From https://aws.amazon.com/blogs/aws/amazon-neptune-a-fully-managed-graph-database-service/, it appears Alexa uses Neptune.
As our product scales, we will want to simplify deployments and database upgrades as much as possible, so having dgraph as a service would probably very interesting. Hopefully creating new instances could play well with container orchestration services (apparently AWS just launched one to compete with GKE, per https://techcrunch.com/2017/11/29/awss-container-service-gets-support-for-kubernetes/).